1. Field of Invention
This invention relates to local area network systems.
2. Background Information
Local area networks (LANs) using wired interconnections have the disadvantage that extensive cabling is required to interconnect the stations. The provision of such cabling is generally inconvenient and gives rise to inflexibility if it is desired to alter the physical locations of the stations. Wireless transmission links, operating at radio frequencies, have been used to replace the cabling interconnections of a LAN. However, certain problems are associated with the use of a wireless transmission link, particularly for LANs in an indoor environment. One problem associated with wireless LANs operated over radio frequency links is that the radio frequency band is a scarce resource. In order to economize with this resource, it is desirable for stations to utilize the same frequency band.
If the application dictates that a large number of stations be interconnected, then, in order to avoid overloading the LAN, it is desirable that groups of stations be interconnected into separate LANs. Such LANs can be interconnected by bridges. Such bridges are well known devices and are the subject of IEEE Standard 802.1D. However, where a single wireless transmission channel is utilized, a problem arises if stations of one LAN have overlapping coverage areas with stations of another LAN. In this situation, interference may arise between stations of different LANs, possibly causing the loss of some transmitted message frames. Although error recovery procedures are available in some circumstances to recover lost frames, such procedures are not always convenient to apply in some practical implementations.